Theoretical/philosophical issues regarding the development of the project

Skype with Solveig Bøe, Simon Emmerson and Øyvind Brandtsegg.

The starting point and main focus of our conversation was the session that took place 20.-21. September in Studio Olavskvartalet, NTNU, and that is the theme of a former post on this blog. That post also contains audio takes and a video where the musicians discuss their experiences. Øyvind told us about what had been going on and about the reactions and reflections of the participants and himself. Simon had seen the video and listened to the takes, and Solveig will look at the material, try to use Merleau-Ponty’s language to describe the interactions going on.

session_jazz_fig

One interesting case is when two (to make the system simple) musicians control each other, where for example the louder an instrument plays, the less effect of some kind on the other instrument, the louder the other instument plays the larger effect on the other. Simon had noted in the documentation that the participating musicians mentioned this (way of controlling each other) could lead to confusion. An analogy to playing football with two footballs was made, and the ball changing colour each time someone touched it. While not entirely similar in timing and pace, the image sheds some light on the added complexity. We discussed how this confusion could be reduced and how this could create interesting music. There is a learning curve involved and this must be tied to getting the musicians to know each other’s interaction patterns well, learning (by doing) how effects are created in each others sounds. Learning by listening and doing. But also by getting visual technical feedback? We all noted that the video documentation from the session made it particularly easy to gain insight into the session. More so than listening to the audio without video. There is an aspect of seeing the physical action, and also seeing the facial and bodily expression of the performers. Naturally, this in itself is not particular to our project, it also can be said of many recordings of performances. Still, since the phenomenon of cross-adaptiveness in the interaction can be a quite hard to grasp fully, this extra dimension of perception seems to help us engage when reviewing the documentation.  That said, the video on the blog post was also very effectively edited by Andreas to extract significant points of interest and points of reflection. The editing also affects the perception of the event significantly of course. With that perspective, of the extra sensory dimension letting us engange more readily in the perception and understanding of the event, how could this be used to aid the learning process (for the performers)? Some of the performers also noted in the session interviews that some kind of visual feedback would be nice to have. Simon thought that visual feedback of the monitoring (of the sound) could be of good help. Øyvind also agrees to this, while at the same time also stressed that it could result in making the interactions between the musicians even more taxing, because they now also had to look at the screen, in addition to each other. Commonly in computer music performance, there has been a concern to get the performer’s focus away from the computer screen as it in many cases has been detrimental to the experience both for the performer and the audience. Providing a visual interface could lead to similar problems. Then again, the visual interface could potentially be used with success during the learning stage, to speed up the understanding of how the instrument (i.e. the full system of acoustic instrument plus electronic counterparts) works.

We discussed the confusion felt when the effects seemed difficult to control, the feeling of “ghostly transformations” taking place, the disturbances of the awareness of themselves and their “place”. Could confusion here be viewed as something not entirely negative too? Some degree of confusion could be experienced in terms of a pregnant complexity, to stimulate curiousness and lead to deeper engagement? How could we enable this flipping of sign for the confusion, making it more of a positive feature than a negative disorientation? Perhaps one aspect of this process is to provide just enough traction for the perception (in all senses) to hold on to the complex interactions. One way of reducing confusion would be to simplify the interactions. Then again, the analysis dimensions in this session were already simplified (just using amplitude and event density), and the affected modulation (relative balance between effects) also relatively simple. With respect to getting traction for perception to grasp the situation, experimentation with a visual feedback interface is definitely something that needs to be explored.

girl-with-mandolin

According to Merleau-Ponty interactions with others are variations in the same matter, something is the same for all participants, even if – and it always is – experienced from different viewpoints. What is the same in this type of interaction? Solveig said that to interact successfully there have to be something that is the same for all of the performers, they have to be directed towards something that is the same. But what could be a candidate for “the same” in a session where the participants interact with each others interactions? The session seems to be an evolving unity encompassing the perceptions and performances of the participants as they learn how ones instruments work in the “network” of instruments. Simon pointed to the book ‘Sonic Virtuality – Sound as Emergent Perception’ (Mark Grimshaw and Tom Garner – OUP 2015), that argues for the fact that no two sounds are ever the same. Neurophysiologically in each brain sounds are experienced differently, so we can’t say really that we hear the same sound. Solveig’s response was that the same is the situation where the participants create the total sound. In this situation one is placed, even if displaced by the effects created on one’s produced sounds. Displacement became a theme that we tried to reflect upon, the being “there” not “here”, by one being controlled by the other instrument(s). The dialectic between dislocation and relocation being important in this connection. Dislocation of the sound could feel like dislocation of oneself. How does amplification (generally in electroacoustic and electronic music) change the perspectives of oneself? How do we perceive the sound of a saxophone and the music performed on it differently when it is amplified so that the main acoustic impression of the instrument is coming to us through speakers? The speakers usually not being positioned in the same location as the acoustic instrument, and even if they were, the acoustic radiation patterns of the speakers would radically differ from the sound coming from the acoustic instrument. In our day and age, this type of sound reproduction and amplification is so common that we sometimes forget how it affects perception of the event. With unprocessed, as clean as possible or “natural” sound reproduction, the percepual effect is still significant. With processed sound even more so, and with the crossadaptive interactions the potential for dislocation and disconnection is manifold. As we (the general music loving population) have learned to love and connect to amplified and processed musics, we assume a similar process needs to take place for our new means of interaction. Similarly, the potential for intentionally exploring the dislocation effects for expressive purposes also can be a powerful resource.

Sound is in the brain, but also in the haptic, visual, auditory, in general, sensual, space. Phenomenologically what is going on in this space is the most interesting, according to Solveig, but the perspective from neuroscience is also something that could bring productive insights to the project.

We returned to the question of monitoring: How much information should the performers get? What should they be able to control? Visualization of big data could help in the interaction and the interventions, but which form should the visualization have? Øyvind showed us an example of visualization from the Analyzer plugin developed in the project. Here, the different extracted features are plotted in three dimensions (x,y and colour) over time. It provides a way of getting insight into how the actual performed audio signal and the resulting analysis correlates. It was developed as a means of evaluating and selecting which features should be included in the system, but can potentially also be used directly by the performer trying to learn how the instrumental actions result in control signals.

 

Brief system overview and evaluation

As preparation for upcoming discussions about tecnical needs in the project, it seems appropriate to briefly describe the current status of the software developed so far.

analyzer_2016_10
The Analyzer

The plugins

The two main plugins developed is the Analyzer  and the MIDIator. The Analyzer extracts perceptual features from a live audio signal and transmit signals representing these features over a network protocol (OSC) to the MIDIator. The job of the MIDIator is to combine different analyzed features (scaling, shaping, mixing, gating) into a controller signal that we will ultimately use to control some effect parameter. The MIDIator can run on a different track in the same DAW, it can run on another DAW, or on another computer entirely.

Strong points

The feature extraction generally works reasonably well for the signals it has been tested on. Since a limited set of signals is readily available during implementation, some overfitting to these signals can be expected. Still, a large set of features is extracted, and these have been selected and tweaked for use as intentional musical controllers. This can sometimes differ from the more pure mathematical and analytical descriptions of a signal. The quality of of our feature extraction can best be measured in how well a musician can utilize it to intentionallly control the output. No quantitative mesurement of that sort have been done so far. The MIDIator contains a selection of methods to shape and filter the signals, and to combine them in different ways. Until recently, the only way to combine signals (features) was by adding them together. As of the past two weeks, mix methods for absolute difference, gating, and sample/hold has been added.

midiator_modules_2016_10
MIDIator modules

Weak points

The signal chain transmission from Analyzer to MIDIator, and then again from the MIDIator to the control signal destination each incurs at least one sample block latency. The size of a sample block can vary from system to system, but regardless of the size used our system will have 3 times this latency before an effect parameter value changes in response to a change in the audio input. For many types of parameter changes this is not critical, still it is a notable limitation of the system.

The signal transmission latency points at another general problem, interfacing between technologies. Each time we transfer signals from one paradigm to another we have the potential for degraded performance, less stability and/or added latency. In our system the interface from the DAW to our plugins will incur a sample block of latency, the interface between Csound and Python can sometimes incure performance penalties if large chunks of data needs to be transmitted from one to the other. Likewise, the communication between the Analyzer and MIDIator is such an interface.

Some (many) of the feature extraction methods create somewhat noisy signals. With noise, we mean here that the analyzer output can intermittently deviate from the value we perceptually assume to be “correct”. We can also look at this deviation statistically, if we feed it relatively (perceptually) consistent signals and look at how stable the output of each feature extraction method is. Many of the features show activity generally in the right register, and a statistical average of the output corresponds with general perceptual features. While the average values are good, we will oftentimes see spurious values with relatively high deviation from the general trend. From this, we can assume that the feature extraction model generally works, but intermittently fails. Sometimes, filtering is used as an inherent part of the analysis method, and in all cases, the MIDIator has a moving exponential average filter with separate rise and fall times. Filtering can be used to cover up the problem, but better analysis methods would give us more precise and faster response from the system.

Audio separation between instruments can sometimes be poor. In the studio, we can isolate each musician, but if we want them to be able to play together naturally in the same room, a significant bleed from one instrument to the other will occur. For live performance this situation is obviously even worse. The bleed give rise to two kinds of problems: Signal analysis is disturbed by the signal bleed, and signal processing is cluttered. For the analysis, it does not matter if we had perfect analysis methods if the signal to be analyzed is a messy combination of opposing perceptual dimensions. For the effect processing, controlling an effect parameter for one instrument leads to a change in the processing of the other instrument, just because the other instruments’ sound bleed into the first instrument’s microphones

Useful parameters (features extracted)

In many of the sessions up until now, the most used features has been amplitude (rms) and transient density. One reson for this is probably that they are concptually easy to understand, another is that their output is relatively stable and predictable in relation to the perceptual quality of the sound analyzed. Here are some suggestions of other parameters that expectedly can be utilized effectively in the current implementation:

  • envelope crest (env_crest): the peakyness of the amplitude envelope, for sustained sounds this will be low, for percussive onsets with silence between evens it will be high
  • envelope dynamic range (env_dyn): goes low for signals operating at a stable dynamic level, high for signals with a high degree of dynamic variation.
  • pitch: well known
  • spectral crest (s_crest): goes low for tonal sounds, medium for pressed tones, high for noisy sounds.
  • spectral flux (s_flux): goes high for noisy sounds, low for tonal sounds
  • mfccdiff: measure of tension or pressedness, described here

There is also another group of extracted features that is potentially useful but still has some stability issues

  • rhythmic consonance (rhythm_cons) and rhythmic irregularity (rhythm_irreg): described here
  • rhythm autocorr crest (ra_crest) and rhythm autocorr flux (ra_flux): described here

The rest of the extracted features can be considered more experimental, in some cases they might yield effective controllers, especially when combined with other features in reasonable proportions